SPC AC 271954

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0254 PM CDT Tue Jun 27 2023

   Valid 272000Z - 281200Z

   ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
   SOUTHERN KANSAS AND FAR NORTHWEST OKLAHOMA ALONG THE BORDER...

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER MUCH OF
   SOUTHERN KANSAS AND NORTHERN OKLAHOMA...AND OVER WESTERN NEBRASKA...

   ...SUMMARY...
   Supercells evolving into a narrow bowing complex appear likely
   across parts of southern Kansas and northern Oklahoma from late
   afternoon through tonight. Very large hail and perhaps a tornado
   will be the main threat initially, followed by potential for a swath
   of destructive wind gusts in excess of 80 mph.

   ...KS/OK area...
   Air mass recovery is being closely monitored in the wake of the
   earlier storms which have moved into central AR. Cool air currently
   resides over northeast OK and southeast KS, but winds have continued
   to veer and warming is underway. Areas of midlevel clouds do exist
   but substantial heating is occurring over much of the area. As such,
   the air mass should continue to destabilize, especially from western
   OK and the Panhandles into southwest KS within the 70s F dewpoint
   axis.

   Midday soundings from AMA show very steep lapse rates through a deep
   layer, approaching 9 C/km from the surface to 500 mb. Stronger mid
   and high-level flow exists just north of this area (40-60 kt at
   DDC), which will support supercells capable of very large hail with
   the activity now forming over northeast NM and southeast CO. These
   storms should merge over time, producing a substantial cold pool
   with a narrow corridor of destructive winds forecast near the KS/OK
   border.

   For more information see MCD 1307.

   ..Jewell.. 06/27/2023

   .PREV DISCUSSION... /ISSUED 1130 AM CDT Tue Jun 27 2023/

   ...Raton Mesa to the Ozarks and Lower MS Valley...
   A stout mid-level anticyclone will remain anchored across central TX
   with a couple of ridge-riding MCSs possible around it. A plume of
   large to extreme buoyancy will become centered from southwest KS to
   the Ark-La-Miss at peak heating amid 70s surface dew points and very
   steep mid-level lapse rates of 8-9 C/km atop the moist axis. A small
   elevated cluster in eastern OK may track southeast along the
   pronounced buoyancy gradient, with a possibility for surface-based
   development downstream of it along the effective front towards the
   Ark-La-Miss. The weak large-scale forcing for ascent lowers
   confidence in the overall scenario, but there is potential for
   multicell clusters to spread southeast into the Lower MS Valley
   later this afternoon. Primary threat will be scattered damaging
   winds.

   Outflow from the morning complex in OK has reinforced the baroclinic
   zone across central to southern OK, but the leading edge of 70s
   surface dew points in southwest OK will advect north into northwest
   OK by late afternoon. Initial thunderstorm development is expected
   by mid afternoon in the Raton Mesa vicinity, and storms will
   subsequently spread into southwest KS and the northern Panhandles by
   early evening. The initial storms will likely consist of a few
   supercells capable of producing very large hail of 2-3 inches in
   diameter. An increase in low-level shear this evening and increasing
   moisture with eastward extent could result in a window of
   opportunity for a tornado or two with the more discrete supercells.
   Thereafter, upscale growth into a small but particularly intense MCS
   appears probable, due to storm interactions/mergers in the very
   steep lapse rate environment and strengthening low-level jet.
   Localized swaths of destructive severe wind gusts from 80-110 mph
   will be possible into tonight across southern KS/northern OK. The
   overall threat will likely remain spatially confined owing to the
   pronounced EML/capping to its south and residual influence of this
   morning's convection, especially with eastern extent towards the
   Ozarks overnight. 

   ...Northwest KS to ND...
   In the wake of elevated morning storms associated with warm
   advection near 700 mb, low-level moisture advection and surface
   heating will contribute to stronger destabilization from northwest
   KS into southwest SD where MLCAPE of 1500-3000 J/kg should be
   common. Farther north, more modest boundary-layer moisture will
   result in MLCAPE of 1000-2000 J/kg. Lee cyclogenesis across eastern
   CO will help sharpen the dryline by late afternoon close to the
   longitude of the CO/KS border, which should focus widely scattered
   thunderstorm development in northwest KS and western KS. Additional
   storms should develop over the Black Hills, with more isolated
   activity also possible into ND. 
    
   With a mid-level jetlet crossing the southern Rockies into the
   central High Plains, relatively long/straight hodographs will favor
   a few intense supercells capable of producing very large to giant
   hail and isolated severe wind gusts centered on western NE. Some
   clustering may occur during the evening as a southerly low-level jet
   intensifies but pronounced MLCIN and lack of instability with
   eastern extent suggest the severe threat should wane into central to
   eastern portions of NE/KS/SD. 

   ...Mid-Atlantic into eastern NY...
   A mid-level trough with embedded perturbations and an associated
   surface cold front will move slowly eastward across NY/PA and toward
   the Mid-Atlantic coast. Lapse rates, buoyancy and vertical shear
   have all been reduced compared to yesterday, in the wake of prior
   widespread convection and as the primary jet moves offshore.  Still,
   slightly cool mid-level temperatures and surface heating with
   residual moisture in cloud breaks could support isolated damaging
   winds in the strongest storms today.

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